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Message-Id: <20190801230810.21570-7-paulmck@linux.ibm.com>
Date: Thu, 1 Aug 2019 16:07:59 -0700
From: "Paul E. McKenney" <paulmck@...ux.ibm.com>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org,
jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 07/18] rcu/nocb: Allow lockless use of rcu_segcblist_restempty()
Currently, rcu_segcblist_restempty() assumes that the callback list
is not being changed by other CPUs, but upcoming changes will require
it to operate locklessly. This commit therefore adds the needed
READ_ONCE() calls, along with the WRITE_ONCE() calls when updating
the callback list.
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
kernel/rcu/rcu_segcblist.c | 30 +++++++++++++++---------------
kernel/rcu/rcu_segcblist.h | 2 +-
2 files changed, 16 insertions(+), 16 deletions(-)
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 700779f4c0cb..0e7fe678b6ac 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -147,8 +147,8 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
rsclp->len_lazy++;
smp_mb(); /* Ensure counts are updated before callback is enqueued. */
rhp->next = NULL;
- *rsclp->tails[RCU_NEXT_TAIL] = rhp;
- rsclp->tails[RCU_NEXT_TAIL] = &rhp->next;
+ WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp);
+ WRITE_ONCE(rsclp->tails[RCU_NEXT_TAIL], &rhp->next);
}
/*
@@ -176,9 +176,9 @@ bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
if (rsclp->tails[i] != rsclp->tails[i - 1])
break;
- *rsclp->tails[i] = rhp;
+ WRITE_ONCE(*rsclp->tails[i], rhp);
for (; i <= RCU_NEXT_TAIL; i++)
- rsclp->tails[i] = &rhp->next;
+ WRITE_ONCE(rsclp->tails[i], &rhp->next);
return true;
}
@@ -214,11 +214,11 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
return; /* Nothing to do. */
*rclp->tail = rsclp->head;
rsclp->head = *rsclp->tails[RCU_DONE_TAIL];
- *rsclp->tails[RCU_DONE_TAIL] = NULL;
+ WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
rclp->tail = rsclp->tails[RCU_DONE_TAIL];
for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--)
if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL])
- rsclp->tails[i] = &rsclp->head;
+ WRITE_ONCE(rsclp->tails[i], &rsclp->head);
}
/*
@@ -237,9 +237,9 @@ void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
return; /* Nothing to do. */
*rclp->tail = *rsclp->tails[RCU_DONE_TAIL];
rclp->tail = rsclp->tails[RCU_NEXT_TAIL];
- *rsclp->tails[RCU_DONE_TAIL] = NULL;
+ WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL);
for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++)
- rsclp->tails[i] = rsclp->tails[RCU_DONE_TAIL];
+ WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_DONE_TAIL]);
}
/*
@@ -271,7 +271,7 @@ void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
rsclp->head = rclp->head;
for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++)
if (&rsclp->head == rsclp->tails[i])
- rsclp->tails[i] = rclp->tail;
+ WRITE_ONCE(rsclp->tails[i], rclp->tail);
else
break;
rclp->head = NULL;
@@ -287,8 +287,8 @@ void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
{
if (!rclp->head)
return; /* Nothing to do. */
- *rsclp->tails[RCU_NEXT_TAIL] = rclp->head;
- rsclp->tails[RCU_NEXT_TAIL] = rclp->tail;
+ WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rclp->head);
+ WRITE_ONCE(rsclp->tails[RCU_NEXT_TAIL], rclp->tail);
rclp->head = NULL;
rclp->tail = &rclp->head;
}
@@ -312,7 +312,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
if (ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
break;
- rsclp->tails[RCU_DONE_TAIL] = rsclp->tails[i];
+ WRITE_ONCE(rsclp->tails[RCU_DONE_TAIL], rsclp->tails[i]);
}
/* If no callbacks moved, nothing more need be done. */
@@ -321,7 +321,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
/* Clean up tail pointers that might have been misordered above. */
for (j = RCU_WAIT_TAIL; j < i; j++)
- rsclp->tails[j] = rsclp->tails[RCU_DONE_TAIL];
+ WRITE_ONCE(rsclp->tails[j], rsclp->tails[RCU_DONE_TAIL]);
/*
* Callbacks moved, so clean up the misordered ->tails[] pointers
@@ -332,7 +332,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])
break; /* No more callbacks. */
- rsclp->tails[j] = rsclp->tails[i];
+ WRITE_ONCE(rsclp->tails[j], rsclp->tails[i]);
rsclp->gp_seq[j] = rsclp->gp_seq[i];
}
}
@@ -397,7 +397,7 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
* structure other than in the RCU_NEXT_TAIL segment.
*/
for (; i < RCU_NEXT_TAIL; i++) {
- rsclp->tails[i] = rsclp->tails[RCU_NEXT_TAIL];
+ WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_NEXT_TAIL]);
rsclp->gp_seq[i] = seq;
}
return true;
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 8f3783391075..f74960f0305c 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -79,7 +79,7 @@ static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
*/
static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
{
- return !*rsclp->tails[seg];
+ return !READ_ONCE(*READ_ONCE(rsclp->tails[seg]));
}
void rcu_segcblist_init(struct rcu_segcblist *rsclp);
--
2.17.1
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